The present invention relates to an adhesion structure for a motor, and more particularly, to an adhesion structure that adheres a magnet and a rotor with an adhesive agent.
In the prior art, a brushless DC motor is used in an electric power steering apparatus. The DC motor includes an adhesion structure that adheres a magnet formed from neodymium, which is a rare earth, to the outer surface of a steel rotor with an adhesive agent.
The thickness of the adhesive agent between the rotor and the neodymium magnet is about 0.03 mm. The neodymium magnet has a linear expansion coefficient of about zero, which is less than that of the steel rotor. The adhesive agent has a linear expansion coefficient that is greater than that of the rotor.
A motor used in an automobile must be capable of withstanding temperatures of a wide range so that the motor can be used under any temperature that the automobile would encounter. In other words, the motor must function normally even when the automobile is driven in arctic or tropical regions. The adhesion structure undergoes performance tests by repeatedly changing the temperature in a range of, for example, minus 40° C. to positive 120° C. to confirm that the motor has the required durability under various temperatures or in environments in which the temperature changes significantly.
In the performance tests, the expansion and contraction of the neodymium magnet is subtle when the temperature changes. However, a change in temperature expands and contracts the rotor and the adhesive agent. As a result, shearing stress is applied to the interface (adhering surface) between the neodymium magnet and the solidified adhesive agent layer. This may lead to exfoliation of the adhesive agent layer.
Accordingly, Japanese Laid-Open Patent Publication No. 60-102854 proposes the application of a resin mold around the neodymium magnet after the neodymium magnet is adhered to the rotor with an adhesive agent. However, the processing of the resin mold takes time and increases the manufacturing cost.
Further, Japanese Laid-Open Patent Publication Nos. 11-89141 and 14-234449 describes filling a groove in a rotor with an adhesive agent to minimize exfoliation. However, exfoliation of the adhesive agent layer may still occur even when using the groove.
It is an object of the present invention to provide an adhesion structure that effectively suppresses exfoliation of an adhesive agent layer.